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BAR HARBOR, Maine — One of Maine’s iconic forest dwellers may just harbor clues that could lead to better treatment and ultimately a cure for human kidney disease.

Researchers at The Jackson Laboratory in Bar Harbor are studying black bear kidneys in an effort to determine how the animals are able to regenerate the organ every year after spending the winter in near kidney failure.

“During hibernation [the bear] kidney is damaged, and the kidney function decreases to a level comparable to that of a human dialysis patient,” said Dr. Ron Korstanje, Jackson Laboratory assistant professor and lead researcher on the bear kidney project. “We know that in humans, a dialysis patient does not recover unless they receive a kidney transplant.”

But bears, somehow, are able to regain full kidney function after coming out of hibernation.

“We do not know how they are able to do that,” Korstanje said. “We are trying to understand what processes are going on in the bear kidneys, allowing them to recover and have perfectly working kidneys again.”

Gaining that understanding, Korstanje said, could help with the discovery of new treatments for human kidney disease.

More than 43 million Americans have chronic kidney disease, costing more than $42 billion a year, nearly a quarter of the country’s Medicare budget.

“Kidney disease is a really big issue in humans,” said Dr. Deborah Eustis-Grandy, chair of the science department at the Maine School of Science and Mathematics in Limestone but who is on sabbatical at The Jackson Lab. “If scientists can figure out how bears regenerate their kidneys, this could lead to avenues for treating kidney disease.”

At first glance, a bear kidney and a human kidney have little resemblance to each other, Eustis-Grandy said.

A human kidney is smooth, uniform and full of capillaries and structures that filter impurities out of the blood as it passes through the organ.

A bear kidney, on the other hand, comprises numerous lobes that each look and act like a miniature human kidney, Eustis-Grandy said.

“The main thing the body is trying to get rid of is a type of waste called urea,” she said. “If it is not removed from the blood, it can build up and become toxic. When people with kidney failure are on dialysis, the main purpose is to remove urea from the blood.”

In the case of hibernating bears, that urea is retained in the bloodstream and serves as a source for protein synthesis as the bears metabolize and live off their fatty stores.

“There is a lot of speculation on what is going on with this,” Eustis-Grandy said. “We do know there is a reduction of blood flow in the [bear] kidneys in the winter, but we don’t know of any documented specific structural [kidney] abnormalities and [documenting] that is one of the things I am trying to do.”

To get all these samples of bear kidneys to study, Korstanje turned to Dr. Rita Seger, adjunct research professor with the University of Maine’s department of animal and veterinary sciences.
Seger has been studying bears since 2005 and joined The Jackson Lab project about a year and a half ago.

“Ron got in touch with me and said he was interested in looking at bears [and] how they reverse kidney deterioration,” she said. “So we started talking about ways to study that.”

Seger’s own work put her in contact with sources for bear kidneys around the state, including registered Maine guides working during Maine’s bear hunt. The guides were given special Jackson bear kidney collection kits with instructions on how to remove and preserve the organs for study.

Moving forward, Seger said she would like to design a collection process for conducting field kidney biopsies on hibernating bears.

That would allow the researchers at Jackson to look at bear kidneys while they are going into failure and before they regenerate.

“I think the potential for that would be very exciting,” Seger said.

The more information they can get from different times of the year, the better, according to Eustis-Grandy.

“I have a bunch of observational data, like the amount of blood in the [bear kidney] capillaries, which appear to change over time and when that particular kidney was harvested,” she said. “But because we don’t know where and when they came from geographically we are not sure how long they had been out of hibernation.”

The beauty of doing the work using the digitized images of the bear kidney tissue, according to Eustis-Grandy, is that they can all be scanned into a computer and viewed from anywhere.

“I’ll be able to get my students at MSSM involved,” she said. “This study is going to last for years [and] it’s going to take a lot of bears. They are going to have to look at a lot of samples [and] this is something we can have a bunch of my students doing for several hours a week.”

There are still a lot of unknowns when it come to bear kidneys and any tangible results to benefit human kidneys are still a long way off, Korstanje said, but his team at The Jackson Lab is excited about the potential.

“All we know is bear kidneys are barely functioning during hibernation and are perfectly functional in the fall,” he said. “But what happens in between — we really have no idea. Finding a cure for kidney disease is certainly the ultimate goal.”